An audio signal processing device 100 includes a period detecting unit 102 for detecting the fundamental period of an input audio signal 101; a square wave generating unit 106 for generating, according to the fundamental period the period detecting unit 102 detects, a square wave 107 whose period is an integer multiple of the fundamental period; an amplitude correction coefficient generating unit 103 for calculating an amplitude correction coefficient 109 approximately equal and proportional to the intensity of the input audio signal 101; a first multiplier 108 for generating an amplitude-corrected square wave 110 by multiplying the square wave 107 by the amplitude correction coefficient 109; and an adder 104 for adding the amplitude-corrected square wave 110 to the input audio signal 101.